Heavy metals on sediments of a Mexican tropical lake: chemical speciation, metal uptake capacity, and chemical states

Mobility and speciation of heavy metals in sediments of Mexican Lake Chapala were assessed through a five-step sequential extraction technique. Metal adsorption capacity of sediments was investigated from each sequential extraction through measurements of their specific surface areas using nitrogen adsorption data. X-ray photoelectron spectroscopy (XPS) was applied to every geochemical fraction to study the chemical metal species present on the surface of sediments. A low risk of detachment to water column was found for all metals, except Zn, Mn, and Fe, although these metals are not considered of high risk to biota. Despite this, the results of this study indicated that there has not been an adequate control from corresponding authorities regarding discharges containing heavy metals. The results of nitrogen adsorption measurements allowed deducing that sediments are mesoporous solids formed mainly by parallel lamellae (clays) composed of aluminosilicates. A clear relationship was observed between specific surface area and the amount of metals obtained by atomic absorption measurements. XPS results indicated that the main chemical states of metals observed were: silicon dioxide (SiO2), aluminum trioxide (Al2O3), iron/silicon oxide (Fe/SiO2), iron (III) oxyhydroxide [Fe(OH)O], aluminosilicate oxide [Al2SiO5], sodium acetate [NaC2H3O2], iron/aluminum oxide [Fe/Al2O3], aluminum hydroxide [Al(OH)3], and iron oxide [Fe2O3].